On Tue, Oct 10, 2017 at 12:47:56PM -0400, Brian Foster wrote:
> XFS uses a fixed reference count for certain types of buffers in the
> internal LRU cache. These reference counts dictate how aggressively
> certain buffers are reclaimed vs. others. While the reference counts
> implements priority across different buffer types, all buffers
> (other than uncached buffers) are typically cached for at least one
> reclaim cycle.
>
> We've had at least one bug recently that has been hidden by a
> released buffer sitting around in the LRU. Users hitting the problem
> were able to reproduce under enough memory pressure to cause
> aggressive reclaim in a particular window of time.
>
> To support future xfstests cases, add an error injection tag to
> hardcode the buffer reference count to zero. When enabled, this
> bypasses caching of associated buffers and facilitates test cases
> that depend on this behavior.
>
> Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx>
Looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> ---
> fs/xfs/xfs_buf.c | 16 ++++++++++++++++
> fs/xfs/xfs_buf.h | 5 +----
> fs/xfs/xfs_error.c | 3 +++
> fs/xfs/xfs_error.h | 4 +++-
> 4 files changed, 23 insertions(+), 5 deletions(-)
>
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index 2f97c12..d481dd2 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -42,6 +42,7 @@
> #include "xfs_mount.h"
> #include "xfs_trace.h"
> #include "xfs_log.h"
> +#include "xfs_error.h"
>
> static kmem_zone_t *xfs_buf_zone;
>
> @@ -2129,3 +2130,18 @@ xfs_buf_terminate(void)
> {
> kmem_zone_destroy(xfs_buf_zone);
> }
> +
> +void xfs_buf_set_ref(struct xfs_buf *bp, int lru_ref)
> +{
> + struct xfs_mount *mp = bp->b_target->bt_mount;
> +
> + /*
> + * Set the lru reference count to 0 based on the error injection tag.
> + * This allows userspace to disrupt buffer caching for debug/testing
> + * purposes.
> + */
> + if (XFS_TEST_ERROR(false, mp, XFS_ERRTAG_BUF_LRU_REF))
> + lru_ref = 0;
> +
> + atomic_set(&bp->b_lru_ref, lru_ref);
> +}
> diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
> index bf71507d..f873bb7 100644
> --- a/fs/xfs/xfs_buf.h
> +++ b/fs/xfs/xfs_buf.h
> @@ -352,10 +352,7 @@ extern void xfs_buf_terminate(void);
> #define XFS_BUF_ADDR(bp) ((bp)->b_maps[0].bm_bn)
> #define XFS_BUF_SET_ADDR(bp, bno) ((bp)->b_maps[0].bm_bn = (xfs_daddr_t)(bno))
>
> -static inline void xfs_buf_set_ref(struct xfs_buf *bp, int lru_ref)
> -{
> - atomic_set(&bp->b_lru_ref, lru_ref);
> -}
> +void xfs_buf_set_ref(struct xfs_buf *bp, int lru_ref);
>
> static inline int xfs_buf_ispinned(struct xfs_buf *bp)
> {
> diff --git a/fs/xfs/xfs_error.c b/fs/xfs/xfs_error.c
> index eaf86f5..6732b0a 100644
> --- a/fs/xfs/xfs_error.c
> +++ b/fs/xfs/xfs_error.c
> @@ -58,6 +58,7 @@ static unsigned int xfs_errortag_random_default[] = {
> XFS_RANDOM_DROP_WRITES,
> XFS_RANDOM_LOG_BAD_CRC,
> XFS_RANDOM_LOG_ITEM_PIN,
> + XFS_RANDOM_BUF_LRU_REF,
> };
>
> struct xfs_errortag_attr {
> @@ -163,6 +164,7 @@ XFS_ERRORTAG_ATTR_RW(ag_resv_critical, XFS_ERRTAG_AG_RESV_CRITICAL);
> XFS_ERRORTAG_ATTR_RW(drop_writes, XFS_ERRTAG_DROP_WRITES);
> XFS_ERRORTAG_ATTR_RW(log_bad_crc, XFS_ERRTAG_LOG_BAD_CRC);
> XFS_ERRORTAG_ATTR_RW(log_item_pin, XFS_ERRTAG_LOG_ITEM_PIN);
> +XFS_ERRORTAG_ATTR_RW(buf_lru_ref, XFS_ERRTAG_BUF_LRU_REF);
>
> static struct attribute *xfs_errortag_attrs[] = {
> XFS_ERRORTAG_ATTR_LIST(noerror),
> @@ -196,6 +198,7 @@ static struct attribute *xfs_errortag_attrs[] = {
> XFS_ERRORTAG_ATTR_LIST(drop_writes),
> XFS_ERRORTAG_ATTR_LIST(log_bad_crc),
> XFS_ERRORTAG_ATTR_LIST(log_item_pin),
> + XFS_ERRORTAG_ATTR_LIST(buf_lru_ref),
> NULL,
> };
>
> diff --git a/fs/xfs/xfs_error.h b/fs/xfs/xfs_error.h
> index 7c4bef3..78a7f43 100644
> --- a/fs/xfs/xfs_error.h
> +++ b/fs/xfs/xfs_error.h
> @@ -107,7 +107,8 @@ extern void xfs_verifier_error(struct xfs_buf *bp);
> #define XFS_ERRTAG_DROP_WRITES 28
> #define XFS_ERRTAG_LOG_BAD_CRC 29
> #define XFS_ERRTAG_LOG_ITEM_PIN 30
> -#define XFS_ERRTAG_MAX 31
> +#define XFS_ERRTAG_BUF_LRU_REF 31
> +#define XFS_ERRTAG_MAX 32
>
> /*
> * Random factors for above tags, 1 means always, 2 means 1/2 time, etc.
> @@ -143,6 +144,7 @@ extern void xfs_verifier_error(struct xfs_buf *bp);
> #define XFS_RANDOM_DROP_WRITES 1
> #define XFS_RANDOM_LOG_BAD_CRC 1
> #define XFS_RANDOM_LOG_ITEM_PIN 1
> +#define XFS_RANDOM_BUF_LRU_REF 2
>
> #ifdef DEBUG
> extern int xfs_errortag_init(struct xfs_mount *mp);
> --
> 2.9.5
>
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